The Malfoys could turn into enemies in this fanfiction. Lucius Malfoy might see Harry's blade master skills as a way for the Potter family to gain more power and influence in the wizarding world. He could plot against Harry. Also, there could be some ancient dark spirits that are awakened by the magic associated with Harry's blade, and they would try to destroy him to regain their own power.
Voldemort or his remaining Death Eaters could be the main enemies. They would see Harry's new blade master abilities as a threat. Another potential enemy could be a dark wizard from a foreign land who is jealous of Harry's power.
The obvious enemies could be the Ministry of Magic. If Harry is stealing things, even if for good reasons, they would see him as a criminal. The Aurors would be sent after him. Another potential enemy could be some of the dark wizards who might want the same items that Harry is after. They would not want Harry to get in their way and would try to stop him or even capture him to get information on the whereabouts of the valuable items.
Some of the dark wizards who are looking for a new source of power might target Harry. They might think that by capturing or controlling him, they can access the powers of Trigon. There could also be entities in other dimensions that see Harry as a key to opening portals between worlds and want to use him for their own malicious purposes.
Alien races that are envious of the Earth - born magic could be enemies. They might see Harry and the wizards as a threat to their own power and dominance in the universe. Also, there could be dark wizards who have escaped to space to avoid the law on Earth and continue their evil deeds, now with a new set of space - related challenges and opportunities.
Voldemort would still be a major enemy. But with Kratos raising Harry, Voldemort might face a much more challenging opponent. Also, any dark wizards or creatures that oppose Harry would be in trouble. Kratos wouldn't tolerate any threats to Harry, so even the Death Eaters would have to be extra careful. Another potential enemy could be those in the wizarding world who oppose Kratos' methods of raising Harry, seeing them as too brutal or un - wizard - like.
The Death Eaters could still be a major threat. Even with Voldemort gone, some of them might be trying to revive the dark ways and see the wizard king as a big obstacle in their path.
There could be a new dark wizard or witch who is jealous of the Potter family's legacy. They might target Harry Potter's daughter to try and bring down the family name and prove their own power.
Another potential enemy could be a group of pure - blood supremacists who don't like the idea of the White Knight, who might be a symbol of change and equality in the wizarding world. They would try to undermine the White Knight's efforts to make the wizarding world more inclusive.
Maybe there could be a group of rogue wizards who believe that Harry's power to be the master of life is an abomination against the natural order of magic. They would oppose him and try to strip him of his power, seeing themselves as the protectors of the 'true' way of magic. Another potential antagonist could be a power - hungry wizard within the Ministry of Magic who is jealous of Harry's new - found abilities and tries to undermine him at every turn.
Another possibility is a reformed dark wizard. Someone who has seen the error of their ways and now uses their in - depth knowledge of dark magic to teach students how to defend against it. This character would have a very interesting backstory, having once been on the wrong side but now using their experiences to help the next generation of wizards in the DADA class.
One problem could be that it misrepresents the values of the original Harry Potter series. The series promotes equality and freedom, and the'slave master' concept is the opposite. Another issue is that it might make some fans uncomfortable, especially those who are sensitive to themes of slavery and oppression.